Numerous discoveries within the field of biomimetic research have led to the recognition that proteins can induce or accelerate precipitation of inorganic materials—both crystalline and amorphous—from aqueous precursors under ambient conditions. In vitro experiments have demonstrated that these same proteins as well as shorter chain peptides that mimic certain regions of the proteins can exhibit these same effects absent any biological context. These findings suggest that synthetic molecules might be discovered that can serve as accelerants of crystallization processes in industrial settings. Moreover, design of molecules that mimic the action of these natural biopolymers but that are much more stable against high pressures, temperatures and acidic conditions would result in a technology that is broadly applicable to industrial crystallization. Some example areas of potential application include pharmaceuticals, non-linear optical crystals, scintillators, and materials for sequestration of metals, radionuclides and CO2.
Conservative and minimally invasive dentistry emphasize the reversal of the caries (tooth decay) process and repair of the damaged tissue as a first step to the long term health of the patient. Enamel remineralization is an accepted phenomenon with established mechanisms related mainly to promotion or remineralization aided by fluoride. Dentin remineralization is also believed to occur in some cases but has proven less tractable because of the complex organic-inorganic composite structure based on collagen type I reinforced with apatite that is found in dentin, cementum and bone. Recent approaches to remineralization of the demineralized dentin matrix show promising results, including substantial restoration of the mechanical properties of hydrated carious tissues, a process we have termed functional remineralization (FR) to distinguish it from simple precipitation of mineral that does not lead to such mechanical recovery. Functional remineralization would enhance the minimally invasive trend in dentistry and preserve substantial tooth structure, providing improved oral health care and lower costs.
Currently, many types of materials have been developed as mineralizing or remineralizing agents for enamel and dentin. Fluoride containing products and fluoridated drinking water are important products in this area as one of their functions is to accelerate remineralization of the partially demineralized enamel structure. Briefly, although not completely understood, enamel development occurs by protein guided growth of apatite mineral in the form of enamel rods. During maturation the very long and thin crystallites of the apatite expand as nearly all of the organic matrix that guided the initial formation of the tissue is resorbed. Thus a highly mineralized and cell-free tissue is left as the outer covering of the teeth. When demineralized by the bacterial process known as caries, the mineral is partially dissolved, but if portions of the minerals are left intact, the crystallites can be rebuilt with calcium and phosphate ions from solutions or saliva, and this process can be accelerated by fluoride treatment.
In dentin and bone the fundamental structure of the tissue is different than in enamel, and is based on collagen type I matrix in which mineral reinforces the collagen within the collagen fibrils themselves (intrafibrillar mineral) and between the collagen fibrils (extrafibrillar mineral). In dentin the formative cells or odontoblasts slowly retreat from the dentin-enamel junction and come line the pulp chamber of the tooth. The cells leave tubule pathways in their wake during tissue formation so that the final dentin structure consists of tubules that are partially filled with cellular processes (tails of the cells) separated by intertubular dentin consisting of the mineralized collagen matrix. In addition a highly mineralized cuff forms around the cellular process known as peritubular dentin, but this portion of the structure does not contain collagen. If the initial coating of enamel on the crown or cementum on the root is lost and open tubules are exposed to the oral environment the tooth will become painful due to fluid movement that stimulates nerve endings associated with cells in the pulp chamber. Thus many products for hypersensitive teeth seek to block the open tubules using various approaches to prevent the fluid movement by precipitation of crystals in the tubule lumen.
Dental caries (decay) also may destroy the dentin structure. If the bacterial products penetrate through the enamel and reach the dentin, the dentin structure is subject to demineralization and deproteinization. Demineralization in dentin is more rapid than in enamel for multiple reasons: the apatite crystallites are smaller, contain more carbonate, and there is less mineral since much of the structure is organic matrix. Therefore, current standards of care require that even early dentin lesions must be treated by surgical intervention and restoration. However, there is significant research directed at strategies that aim at remineralization of dentin and most of these are focused on supplying additional calcium and phosphate ions from pastes that release these agents in close proximity to the demineralized area. Newer treatments that show promise now include adjunctive agents that provide the possibility of restoring the mineral within both the intrafibrillar and extrafibrillar compartments of dentin tissue. One such approach is the polymer-induced liquid-precursor (PILP) process that appears to aid the delivery of the ions in the form of nanoclusters to the collagen fibrils and leads to penetration of the collagen and formation of apatite after deposition of amorphous calcium phosphate.